feat: Implement UVM Dashboard with frontend and backend integration

- Added dashboard.js for frontend functionality, including VM management and system health monitoring.
- Created dashboard route to serve the dashboard HTML.
- Introduced diagnostics route for token-protected host diagnostics.
- Enhanced VMs router with bulk actions, VM log retrieval, and port management.
- Updated lifecycle service to read VM log tails with truncation handling.
- Integrated static file serving for dashboard assets in the FastAPI server.
- Redirect root URL to the dashboard for improved user experience.

uvm/lifecycle.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import os
 import re
 import shutil
 import time
@@ -39,6 +40,15 @@ class OperationResult:
     error: str | None = None
 
 
+@dataclass(frozen=True, slots=True)
+class LogTail:
+    content: str
+    truncated: bool
+
+
+_MAX_LOG_TAIL_BYTES = 262_144
+
+
 class LifecycleService:
     """All mutating entry points use operation lock -> short state transaction."""
 
@@ -415,6 +425,41 @@ class LifecycleService:
         self._validate_paths(vm)
         return Path(vm.log)
 
+    def read_log_tail(self, identifier: str, *, tail: int) -> LogTail:
+        """Read a bounded tail from a validated VM log without following it."""
+        if type(tail) is not int or tail < 0:
+            raise ValidationError("log tail must be a non-negative integer")
+        path = self.log_path(identifier)
+        try:
+            with path.open("rb") as stream:
+                end = stream.seek(0, os.SEEK_END)
+                if tail == 0:
+                    return LogTail(content="", truncated=False)
+                start = max(0, end - _MAX_LOG_TAIL_BYTES)
+                previous = b""
+                if start:
+                    stream.seek(start - 1)
+                    previous = stream.read(1)
+                stream.seek(start)
+                content = stream.read(end - start)
+        except OSError as error:
+            raise UvmError("could not read VM log") from error
+
+        truncated = False
+        if start and previous != b"\n":
+            newline = content.find(b"\n")
+            if newline == -1:
+                truncated = True
+            else:
+                content = content[newline + 1:]
+        lines = content.splitlines(keepends=True)
+        if start and len(lines) < tail:
+            truncated = True
+        return LogTail(
+            content=b"".join(lines[-tail:]).decode("utf-8", errors="replace"),
+            truncated=truncated,
+        )
+
     def diagnostics(self) -> list[dict]:
         checks = [("root", require_root), ("kvm", check_kvm),
                   ("Firecracker", self._verify_firecracker),